Microstructure and deformation behavior of a novel steel rebar: Effect of the heterogeneous microstructure of soft ferrite and Hard bainite
Dan Song, Guowei Wang, Falin Yang, Huande Chen, Ningning Liang, Han Ma, Jinghua Jiang, Xiaolong Ma
Abstract
This study reports a detailed investigation of the deformation behavior and microstructural evolution of a novel ultra-low carbon Cr-Mo alloyed dual-phase steel rebar aimed for marine applications. The rebar matrix consists of the lamellar ferrite/bainite dual phases with the lamellar interfaces along the rolling direction. The soft ferrite phase is composed of larger grains with a low dislocation density, while the hard bainite phase is composed of finer grains with a much higher dislocation density. By comparing the strain hardening behavior from different sites at the rebar with varying ferrite and bainite volume fractions, it shows that the hetero-deformation induced (HDI) hardening is strong and dominates the overall work hardening behavior in the early stage of plastic deformation by prevailing over the conventional sum-up of contribution of each phase alone. In this stage, the plastic deformation of ferrite was constrained by the disproportionally-strained, neighboring bainite, creating the accumulation of geometrically necessary dislocations (GNDs) at the phase interface and the long-range HDI stress. The results also reinforce the understanding of deformation behavior of dual-phase steels, especially around the role of HDI stress and hardening.